22: Metals
- Page ID
- 49645
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Approximately three-quarters of the known elements are metals and conduct both heat and electricity very well. Morevoer, they have shiny surfaces; they are capable of being shaped by hammering (malleable) and also of being drawn into wires (ductile). These properties can be understood in terms of metallic bonding in which valence electrons are delocalized over an entire metallic crystal. The strength of metallic bonding varies roughly as the number of electrons available in this sea. Chemical properties of the metals include a tendency to lose electrons and form positive ions, and the ability of their oxides to function as bases. The extent of these characteristics varies from one metal to another.
- 22.1: Prelude to Metals
- Chemical properties of the metals include a tendency to lose electrons and form positive ions, and the ability of their oxides to function as bases. The extent of these characteristics varies from one metal to another. Several borderline cases such as B, Si, Ge, As, Sb, and Te are difficult to classify as metals or nonmetals. These elements are usually referred to as the metalloids or semimetals.
- 22.2: Metallic Bonding
- Electrons can be fed into one end of a metal wire and removed from the other end without causing any obvious change in the physical and chemical properties of the metal. To account for this freedom of movement modern theories of metallic bonding assume that the valence electrons are completely delocalized; that is, they occupy molecular orbitals belonging to the metallic crystal as a whole. These delocalized electrons are often referred to as an electron gas or an electron sea.
- 22.3: Metallurgy
- The processing of ores may be divided into three steps. (1) Concentration to remove worthless material (gangue) or to convert the mineral into an appropriate form for subsequent processing. (2) The most-important step is reduction of the metal from a positive oxidation state. This may involve elevated temperatures, chemical reducing agents, electrolysis, or some combination of these treatments. (3) Refining is required to achieve the purity desired in the final product.
- 22.4: Beneficiation
- Beneficiation is any process which removes the gangue minerals from ore to produce a higher grade product, and a waste stream. Beneficiation may involve physical or chemical processes. Often, as in the case of panning for gold, the desired ore or metal is denser than the gangue. The latter can be suspended in a stream of water and flushed away.
- 22.5: Reduction of Metals
- The ease with which a metal may be obtained from its ore varies considerably from one metal to another. Since the majority of ores are oxides or can be converted to oxides by roasting, the free-energy change accompanying the decomposition of the oxide forms a convenient measure of how readily a metal may be obtained from its ore.
- 22.6: Refining of Metals
- Once a metal is reduced, it is still not necessarily pure enough for all uses to which it might be put. An obvious example is the brittleness and low tensile strength of pig iron, characteristics which make it suitable for casting, but little else. Steelmaking involves oxidation of the impurities in basic oxygen, open hearth, or electric furnaces.
- 22.7: Corrosion
- An important aspect of the use of some metals, particularly of iron, is the possibility of corrosion. It is estimated that about one-seventh of all iron production goes to replace the metal lost to corrosion. Rust is apparently a hydrated form of iron(III)oxide. Rusting requires both oxygen and water, and it is usually sped up by acids, strains in the iron, contact with less-active metals, and the presence of rust itself.
- 22.8: Coordination Compounds
- A characteristic feature of the transition metals is their ability to form a group of compounds called coordination compounds, complex compounds, or sometimes simply complexes.
- 22.10: Chelating Agents
- Chelating agents are ligands that are able to form two or more coordinate covalent bonds with a metal ion. An important and interesting example of this is the chelating agents—ligands which are able to form two or more coordinate covalent bonds with a metal ion. One of the most common of these is 1,2-diaminoethane (usually called ethylenediamine and abbreviated en.) For metals which display a coordination number of 6, an especially potent ligand is ethylenediaminetetraacetate ion (EDTA).